1. Field of the Invention
The invention pertains to magnetic disc memories and more particularly to magnetic disc memories for digital computers adapted for application in an environment where the memory is subjected to substantial vibration, wide variations in temperature and humidity and where mass and volume must be kept at a minimum, such as airborne applications.
2. Description of the Prior Art
The subject invention is an improvement over the device disclosed in copending application Ser. No. 381,817 now U.S. Pat. No. 3,864,748 entitled "Magnetic Disc Memory" of Craig T. Herdman et al., filed July 23, 1973 and assigned to the assignee of the present invention. The invention of Ser. No. 381,817, although representing a significant improvement in the art of magnetic disc memories, is nonetheless subject to certain limitations. To begin with, the location of the electrical drive motor in this invention adds to the total volume of the memory and creates an unsymmetrical configuration. Secondly, since the disc is mounted to an arbor which extends from the electrical drive motor, the bearings of the motor are subjected to a bending moment due to the cantilevered structure resulting in increased wear thereon. Thirdly, because the electrical drive motor must be kept as small as possible to minimize the external volume, minimum bearing separation must be maintained thereby hindering the bearing alignment.
The memory capacity of the prior art device is limited to approximately one million bits due to several factors. Firstly, only one side of the magnetic disc is being utilized for the storage and retrieval of information. Secondly, maximum utilization of the magnetizable surface of the magnetic disc is not being achieved. Thirdly, a symmetrical configuration of this memory, specifically with respect to the location of the electrical drive motor, inhibits the use of both sides of the magnetic disc with regard to utilizing common parts and assemblies.
The alignment of the spring mechanism, which urges the read/write head assemblies to the magnetizable surface of the magnetic disc without producing pitching moments introduces another limitation into this device. In the prior art memory, a button with a flat top is located at the center of buoyancy of the read/write head assembly. To prevent pitching moments from developing, the spring must align almost exactly with the center of the flat-top button. In practice, this alignment often proves to be time consuming and may eventually deteriorate.
The extension and retraction mechanism, incorporated to extend and retract the read/write head assemblies toward and away from, respectively, the surface of the magnetic disc, introduces a pair of limitations. Firstly, they add substantial complexity in cost of the support mechanism for the read/write head assemblies. Secondly, they require the addition of magnetic coils and a plate (which acts as an armature) to operate the mechanisms. This complicates the design, and increases the cost, the volume, and the mass of the memory.
The present invention overcomes all of the aforementioned limitations while maintaining all the significant improvements of the prior invention. Additionally, the present invention discloses additional features to improve the symmetry of the memory, reduce the volume and increase the storage capacity.